DE102005016067A1 - Method for increasing the start reproducibility during start-stop operation of an internal combustion engine - Google Patents

Abstract

The present invention relates to a method for increasing the start-reproducibility during start-stop operation of an internal combustion engine of a motor vehicle with start optimization. The start reproducibility is increased by reducing a maximum speed gradient attainable for different stop positions of the internal combustion engine to a defined speed gradient.

Description

The The present invention relates to a method for improving the Start optimization of the internal combustion engine of a motor vehicle, the used in start-stop operation.

Around to reduce the fuel consumption in motor vehicles takes place at Standstill of the motor vehicle stopping or stopping the internal combustion engine followed by a restart as soon as the motor vehicle continues should drive. This start-stop operation comes with a startup optimization used, which allows starting the internal combustion engine, even before synchronization with the crankshaft occurred Has. requirement for the start optimization is the knowledge of the engine position after the Stopping the internal combustion engine, so that when detecting a first Tooth flank of the crankshaft sensor the current engine position up to Synchronization can be determined by incrementing. To the synchronization will start in conventional Way continued.

The different speed curves of a high-revving internal combustion engine with direct injection, which is operated with or without start optimization, are in 1 shown. The dashed curve shows a speed curve for operation without start optimization, while the solid curve represents the speed curve for operation with start optimization. The speed curves are plotted on the same time axis, so that a direct time comparison of both speed curves is possible. It can be seen that at the time t = 430 ms, the internal combustion engine with start optimization tion has already reached idle speed, while the internal combustion engine ignites with conventional start strategy for the first time at this time. The curve for operation with start optimization shows strong speed fluctuations during startup. These variations arise due to the effects of compression work to be performed by the cylinder, friction, and discontinuous momentum release. Such a start-stop operation is by the DE 43 04 163 A1 reveals their startup optimization in 2 is shown. It can be seen that the different cylinder fillings of the first combustion, for example in a four-cylinder internal combustion engine during start optimization, ie before synchronization, depend on the stop position of the internal combustion engine. In an internal combustion engine with more than four cylinders, several first burns during the start optimization are possible, which influence the starting behavior of the internal combustion engine. The dependence on the stop position arises in particular for directly injecting internal combustion engines. Because only with direct injection after closing the intake valve fuel can still be introduced into the combustion chamber and thus a combustion of a dependent of the stop position cylinder filling can be realized. In the case of intake manifold injectors, by contrast, the injection at the end of the intake phase is completed, so that a maximum cylinder charge for the first combustion always results during the start optimization of a port injector.

As 2 shows, depending on the stop position of an internal combustion engine with four cylinders one or more burns during the start optimization possible. The stop positions and the positions discussed further herein are given as crankshaft angles, respectively. These burns make due to their cylinder fillings the varying speed curve to synchronization. Due to these varying starting conditions of the respective combustion during the start optimization, chemical energy is not reproducibly converted into kinetic energy. This is exemplary in 3 shown comparing the speed curves and the spin accelerations of a start of the internal combustion engine starting from a stop position of 45 ° after top dead center and 90 ° after top dead center. It is apparent that the spin with about 4500 U · min ^-1 · ^{s -1} at a stop position of 45 ° after top dead center is almost twice as large as the spin of 2600 U · min ^-1 · ^{s -1} at a Stop position of 90 ° after top dead center. This different dynamics during the start optimization leads just in vehicles with longitudinally installed internal combustion engine due to the angular momentum conservation to a counter-torque that acts on the vehicle longitudinal axis. Depending on the stop position, this counter-torque varies in size and generates a corresponding tendency to roll of the Kraffahrzeugs. The driver of the motor vehicle will perceive this tendency to roll as a "disturbance" in the motor vehicle or as a disturbance of his "starting feeling". For the driver's well-being, therefore, a reproducibility of the starting behavior of an internal combustion engine regardless of its stop position in the start-stop operation is required.

It is therefore the object of the present invention to provide a method for increasing the starting Reprodu zierbarkeit an internal combustion engine of a motor vehicle with start optimization to provide.

The The above object is defined by the independent claim 1 Procedure solved. Advantageous embodiments and further developments of the method are set forth in the following description and in the dependent claims.

The present method is directed to that in the context of startup optimization an internal combustion engine in start-stop operation a reproducible starting behavior the internal combustion engine or a start-reproducibility generated will be the start-stop operation for the user of the motor vehicle as comfortable as possible to design. It increases the starting reproducibility, starting from a stop position the internal combustion engine first a possible one maximum speed gradient for the first or the first burns in the start optimization phase is calculated. Whether during the startup optimization phase only one or a plurality of first Burns to consider is, depends on the number of cylinders of the internal combustion engine and thus each possible in the different cylinders first combustion before synchronization. This maximum speed gradient results from the optimal utilization of the at this stop position the internal combustion engine possible maximum cylinder filling with fuel and air as well as from the implementation of this cylinder filling with Help of an optimum ignition angle.

There with the present invention just not the maximum possible Speed gradient of the first combustion or burns during the Start optimization is to be realized in another Step the maximum speed gradient to a specified speed gradient reduced, for different Stop positions of the internal combustion engine can be realized. The specified Speed gradient is chosen such that he most frequently the maximum speed gradient occurring stop position of the considered internal combustion engine corresponds. Because the most common occurring stop position by the characteristics of the internal combustion engine is influenced, the specified speed gradient for different Internal combustion engines be different. The speed gradient of a Stop position, before the stop position of the set speed gradient, i.e. at a smaller crankshaft angle, can by the following described method reduced to the specified speed gradient become. But it can also occur a stop position after the most common occurring stop position is. In this case, the speed gradient can the first combustion does not reach the specified speed gradient be increased. For this reason, a fixed one is preferred Speed gradient selected, that of a stop position with a larger crankshaft angle as the most common Stop position of the internal combustion engine corresponds. The specified Speed gradient can therefore despite different stop positions be generated because the maximum speed gradient of each Stop position greater or is equal to the specified speed gradient. Reduce it now specifically the respective maximum speed gradient on the specified speed gradient, receives one the desired one Reproducibility. This reproducibility during the start optimization ensures the user of the motor vehicle, a uniform behavior of the internal combustion engine and in this way a comfortable "starting feeling." The maximum speed gradient can be reduced to the specified speed gradient by with the aid of a retard angle retardation the efficiency of the first burn or the first burns and / or with an intake valve retard cylinder filling for the first or first burns targeted to the desired Value is adjusted.

to Simplification and acceleration of the procedure will be carried out according to a embodiment on a map for resorted to the maximum speed gradient, which is the maximum Speed gradients with optimum ignition angle and optimum fuel quantity dependent on from the stop position of the engine and an engine temperature reproduces. This maximum speed gradient to be taken from the map is then with a for various stop positions specified speed gradients into Relationship set, about it set the efficiency of the first combustion or burns of the start optimization to be able to. This ratio forms the ignition angle efficiency, indicating how strong the maximum possible speed gradient for the present Stop position must be reduced to a reproducible and for the driver pleasant "starting feeling" of the motor vehicle to achieve.

Should the internal combustion engine with an adjustment of the times for opening and Shut down the intake valves work, in this way also the for one certain stop position of the internal combustion engine achievable maximum Speed gradient to be adjusted. In this embodiment of the present method becomes the intake valve retard also taken into account in the calculation of the ignition angle efficiency.

Finally, in order to reduce the efficiency of the first combustion / burns during the start optimization in a targeted manner, an ignition angle offset is calculated from the ignition angle efficiency in order to calculate the ignition timing the optimum firing angle of the first combustion or burns is shifted late. In this way, although the efficiency of the combustion is reduced during the start optimization, but at the same time the required for a pleasant "starting feeling" reproducible piston forces are ensured.

The accompanying drawings show:

1 a comparative representation of the engine speed for an internal combustion engine with start optimization and an internal combustion engine without start optimization,

2 the representation of a start optimization with a stop position defined with respect to the ignition TDC, as known from the prior art,

3 the comparison of the first start-optimized ignition at the stop position of 45 ° after top dead center and at the stop position of 90 ° after top dead center.

When parking a motor vehicle, the internal combustion engine stops randomly in different _stop positions α _stop . Depending on the throttle opening, this results in a mean parking position of about 90 ° crankshaft angle after top dead center. The occurring stop positions are approximately gauss distributed over this assumed central position angle. However, it is also conceivable that internal combustion engines, due to their structure, their number of cylinders or due to other configuration data, show a different middle parking position α _stop .

Around the reproducibility of the starting behavior in dependence from the stop position, d. H. for a variety of stop positions an internal combustion engine repeatedly the same speed gradient when restarting, a method is used with the efficiency of the first combustion of the start optimization - ie the Burns before synchronization - specifically reduced. This The procedure can also affect a majority of first burns extend the startup optimization, as with a multi-cylinder Internal combustion engine can occur. This will be an approximately constant Speed gradient generated from any stop position, because they have the same or a larger cylinder filling than one below closer explained Target stop position (reference position) has.

The Efficiency of combustion during The start optimization is on the one hand about the adjustment of the ignition angle or otherwise in the cylinder available set the amount of static air. It is also preferred, both Setting method for the control of the start-stop operation of an internal combustion engine combined to use.

First, as a basis for the present method, the determination of the _stop position α _stop the internal combustion engine, for example by means of a crankshaft sensor. This crankshaft sensor detects the crankshaft angle even after switching off the internal combustion engine. The _stop position α _stop determines the achievable by the internal combustion engine maximum speed gradient ω _{max of} the first combustion / burns for which there is no complete cylinder filling, when the internal combustion engine is restarted during the start optimization. The maximum speed gradient ω _max is obtained starting from the _stop position α _stop , which stops at this _stop position α possible optimal cylinder filling with air and fuel and the assumption that this cylinder filling is ignited at an optimal ignition angle. Other parameters for determining the maximum speed gradient ω _max may also be taken into account, such as, for example, the engine temperature TCO or a variable representing the engine temperature, for example the temperature of the coolant of the engine. According to one embodiment, the maximum speed gradient is determined as a function of the stop position and the engine temperature ω _max = ω _max (α _stop , TCO) assuming an optimal injection amount, an optimal ignition angle and an optimal intake valve closing.

In order to limit the overhead for calculating the maximum speed gradient ω _max by the operation control unit of the internal combustion engine, the corresponding α the stop position _stop possible maximum speed gradient ω _max is preferably not constantly recalculated, but read out from a stored map. Such a map can for example be determined empirically for each type of internal combustion engine and then stored in the operating control unit. From the preferred map, after determining the _stop position α _stop and the temperature TCO of the internal combustion engine, the corresponding maximum speed gradient ω _{max is} read, while also the above assumptions apply.

In order to bring the achievable due to the different _stop positions α maximum speed gradient ω _max to a common speed gradient level, the target _stop position α _stop- set set. This target _stop position α _stop-soll is characterized by the fact that the generally usual _stop positions α _stop the internal combustion engine at or before this position. Although a small proportion of the stop positions may be behind the target stop position, the target stop position is selected such that an effective start optimization is achieved with short start times. Based on this selection, it is ensured that the maximum speed gradient which can _be reached starting from the setpoint _stop position α _is not exceeded from each stop or run-out position of the internal combustion engine. This is done with optimum cylinder filling and optimum ignition angle when the _stop position α _stops with the set _stop position α _{stop-should stop} at a _stop position α less than the set _stop position α _Stopp-soll results in a larger cylinder filling compared to the set stop position ( Reference position), so that with reduced efficiency of the first combustion / burns, the maximum speed gradient of the target _stop position α _stop- set is set. This maximum speed gradient, which can be achieved from the setpoint _stop position α, _{should be reached} under optimal conditions, and is referred to as a defined speed gradient. It is likewise preferred to define the defined rotational speed gradient as a function of further operating parameters of the internal combustion engine, such as a desired engine temperature TCO _soll .

mit α_stopp ≤ α_stopp-soll,

η_IGA

Zündwinkelwirkungsgrad,

α_Stopp

Stoppposition,

TCO

Motortemperatur,

TCO_SOLL

Motorsolltemperatur

ω_max

maximaler Drehzahlgradient,

α_stopp-soll

Soll-Stoppposition.

If the _stop position α _stop before the target _stop position α _stop-soll , as it is due to the choice of the target _stop position α _stop- for example, 90 ° after top dead center, can via a reduction in the Zündwinkelwirkungsgrads η _IGA the speed gradient the first combustion during the start optimization to the maximum speed gradient corresponding to the target _stop position α _{stop-soll should be} reduced. Furthermore, a deviation of further operating parameters of the internal combustion engine from its desired value can be compensated by means of the reduction of the ignition angle efficiency. An example of this is the engine temperature TCO whose deviation from the target engine temperature TCO _{is to be} compensated. The ignition angle efficiency η _{IGA is} calculated as a function of the _stop position α _stop and the motor temperature TCO according to the following quotient:

with α _stop ≤ α _stop-soll ,

η _IGA

ignition angle,

α _stop

Stop position,

TCO

Engine temperature,

TCO _SHOULD

Motor nominal temperature

ω _max

maximum speed gradient,

α _stop-soll

Target stop position.

According to a further embodiment of the present method, the speed gradient can be adjusted not only via the Zündwinkelwirkungsgrad and the subsequent Zündwinkelverstellung, but also on the adjustment of the amount of air in the cylinder. This adjustment can be applied alone or in combination with the retard of the ignition angle. The amount of air that is compressed in the cylinder in the first compression stroke can be reduced by an adjustment of the intake camshaft late. If the internal combustion engine stopped in a _stop position α _stop at bottom dead center, a maximum cylinder filling would result with air and fuel and thus also a possible maximum speed gradient. If the intake camshaft is now set to maximum, so that closing of the intake valve takes place, for example, 70 ° after bottom dead center, then part of the air is pushed back into the intake pipe during the compression stroke until the intake valve (EVS) closes. In this way, for a _stop position α _stop before the closing of the intake valve EVS a _stop independent of the _stop position α cylinder filling can be set, which is adjusted by closing the intake valve. The achievable speed gradient corresponds in this case a _stop position α _stop , which is equal to the closing position of the intake valve EVS (see the formula below). The above-described influencing the cylinder filling via an adjustment of the intake camshaft requires an adjustment that can be operated even when the internal combustion engine. This is possible, for example, with electric camshaft actuators or with an electric valve control in camshaft-free internal combustion engines.

für α_stopp ≤ α_stopp-soll,
und EVS ≤ α_stopp-soll,

η_IGA

Zündwinkelwirkungsgrad,

α_stopp

Stoppposition,

TCO

Motortemperatur,

TCO_SOLL

Motorsolltemperatur

ω_max

maximaler Drehzahlgradient,

α_stopp-soll

Soll-Stoppposition,

If, as described above, the cylinder charge is reduced by late closing of the intake valve, the _stop position α _{stop is} defined by the closed position EVS of the intake valve, since only the Schließpo sition defines the cylinder filling and the maximum speed gradient ω _{max possible} under optimum conditions. Applied to these boundary conditions of the internal combustion engine, the ignition angle efficiency already mentioned above can also be calculated here using the following equation.

for α _stop ≤ α _stop-soll ,
and EVS ≤ α _stop-soll ,

η _IGA

ignition angle,

α _stop

Stop position,

TCO

Engine temperature,

TCO _SHOULD

Motor nominal temperature

ω _max

maximum speed gradient,

α _stop-soll

Target stop position,

EVS closed position of the inlet valve.

From the ignition angle efficiency defined in the above equations, an ignition angle offset Δ _IGA for the first combustion is finally calculated. This ignition angle offset is a function of the ignition angle efficiency η _IGA , the _stop position α _stop and the engine temperature TCO, so that the relationship Δ _IGA = Δ _IGA (η _IGA , α _stop , TCO). This firing angle offset shifts the firing angle late in an expected maximum speed gradient of the _stop position α _stop that would be above the set speed gradient. In this way, the efficiency of the first combustion is reduced and thus the actually achieved speed gradient is reduced to the level of the specified speed gradient.

Claims (8)

A method of increasing start-up reproducibility during start-stop operation of an internal combustion engine of a motor vehicle with start-up optimization, comprising the following steps: a. Detecting a _stop position α _{stop of} the internal combustion engine, b. Determining a maximum speed gradient ω _max possible with a first combustion of the start optimization as a function of the _stop position α _stop , an amount of fuel present in a cylinder of the internal combustion engine and an amount of air present in the cylinder at an optimum ignition angle and c. Reduce the maximum speed gradient to a fixed speed gradient, which is reproducible for different _stop positions α _stop by using a Zündwinkel retardation, the efficiency of the first combustion or burns and / or targeted with an intake valve retard the cylinder filling for the first combustion or first burns is reduced. Method according to claim 1, with the further step of: reading out a characteristic map for the maximum speed gradient ω _max , which stops a maximum speed gradient ω _max (α _stop , TCO) with optimum ignition angle and optimum fuel quantity as a function of the _stop position α and an engine temperature TCO Internal combustion engine indicates. Method according to Claim 1 or 2, in which the defined rotational speed gradient is defined by the maximum rotational speed gradient ω _max at a specified target _stop position α _{stopp-soll of} the internal combustion engine. Method according to claim 3, with the further step: determining the ignition retardation for _stop positions α _stop ≤ α _stop-soll from an ignition angle efficiency η _IGA , which stops as a quotient of the specified rotational speed gradient as a function of the desired stop position α _{. to} and a target-engine temperature TCO _Soll and the maximum speed gradient ω _max as a function of the stop position α _stop and the engine temperature TCO according to the following formula results:

Method according to claim 3, with the further step: Reducing available for the first combustion cylinder filling by means of the intake valve retard, whereby the maximum speed gradient is reduced. A method according to claim 5, wherein in the intake valve retard, the _stop position α _{stop is} determined by a closed position EVS of the intake valve with α _stop = EVS. A method according to claim 6, further comprising the step of: determining retard retardation upon application of retard valve retard position α _stop ≤ α _stop-soll and closing position EVS ≤ α _stop-soll from firing angle efficiency η _IGA which is as a quotient of the specified speed gradient as a function of a setpoint engine temperature TCO _soll and the maximum speed gradient ω _max as a function of the _stop position α _stop and the engine temperature TCO results according to the following formula:

A method according to claim 4 or 7, further comprising the steps of: determining the retard retardation for the first combustion with the aid of an ignition angle offset Δ _IGA via the function Δ _IGA = Δ _IGA α _stop , TCO) and shifting the optimum ignition angle of the first combustion about the ignition angle offset towards late.